Although the core characteristics associated with autistic traits are impaired social interactions, there are few studies examining how autistic traits translate into prosocial behaviour in daily life. The current study explored the effect of autistic traits on prosocial behaviour and the mediating role of multimodal empathy (trait empathy and state empathic concern). The results showed that autistic traits reduced prosocial behaviour directly and indirectly through complex mediation by multimodal empathy. The findings revealed the internal mechanism of autistic traits impeding prosocial behaviour and expanded our understandings of social behaviour in autism spectrum conditions (ASCs) and autistic traits in the general population. Furthermore, the results have implications for social adaptability interventions for individuals with ASCs and high levels of autistic traits.